The present invention relates to a light-emission control apparatus and a camera apparatus, each having a light-emitting means for emitting light, which is controlled in accordance with the light reflected from an object of photography. The invention also relates to a method of controlling emission of light applied to an object of photography.
Strobolight photography is performed in some cases in order to take clear-cut photographs. Strobolight photography is achieved by using a light-emitting device such as a strobolight. The emission of light from the light-emitting device is controlled to accomplish optimal strobolight photography.
FIG. 1 illustrates a conventional light-emission control system designed for use in strobolight photography. The system shown in FIG. 1 is operated in the following way to effect strobolight photography.
A light-emitting device 102 starts emitting light in response to a light-emission request made by the microprocessor unit (MPU) incorporated in a camera apparatus. A light-receiving element 103 receives the light reflected from an object 200 of photography. The output of the light-receiving element 103 is supplied to capacitors 104 and 105 and stored therein in the form of an electric charge. A voltage V1 that corresponds to the electric charge stored in the capacitors 104 and 105 is compared with a reference value Vs. When the voltage V1 reaches the reference value Vs, a comparing section 106 outputs a light-emission stop request. Upon receipt of the light-emission stop request the light-emitting device 102 stops emitting light, thereby controlling the emission of light. A resistor 107 determines the current accumulated by the capacitors 104 and 105. It should be noted that the capacitor 105 is connected to the ground by a switch 108. The switch 108 is changed over under the control of the microprocessor unit 101. When the switch 108 is so changed over, the capacitance of the charge-accumulating section is changed, thereby altering the characteristic of voltage transition to the reference value Vs.
FIG. 2 shows how the voltage V1 changes with time. FIG. 3 illustrates how the voltage V1 changes when the light-emitting device 102 stops emitting light. The comparing section 106 generates a light-emission stop request when the voltage V1 reaches the reference value Vs. As seen from FIG. 3, the voltage V1 ceases to change when the light-emitting device 102 stops emitting light in response to the light-emission stop request.
In the conventional light-emission control system, the capacitors 104 and 105 and the comparing section 106 constitute a section for detecting the amount of light the light-receiving element 103 receives. The capacitors 104 and 105 and the section 106 process analog data. Inevitably, the precision of the light-emission control greatly depends on the characteristics of the capacitors 104 and 105, the discharging of these capacitors and the performance of the comparing section 106.
Since the capacitors 104 and 105 and the comparing section 106 are major components of the light-emission control system, the operation characteristics of the system must be adjusted by using additional circuit components such as a variable resistor or an electronic volume during the manufacture of the system. The adjustment of operation characteristics is cumbersome and will increase the manufacturing cost of the light-emission control system.
Further, it is desired that the degree of freedom of controlling the light-emitting device 102 be enhanced to increase the precision of the light-emission control.
The present invention has been made in view of the foregoing. The object of the present invention is to provide a light-emission control apparatus, a camera apparatus and a light-emission control method, which can control the emission of light with high precision and at low cost and which can increase the degree of freedom of controlling the light-emitting device used.
To achieve the object, a light-emission control apparatus according to the invention comprises: light-receiving means for outputting a light-reception signal corresponding to an amount of light received; analog-to-digital converting means for converting the light-reception signal to digital data; and control means for outputting a light-emission stop request to light-emitting means, thereby causing the light-emitting means to stop emitting light, when an integrated value obtained by integrating the digital data reaches a predetermined threshold value.
In the light-emission control apparatus, the light-emission stop request is output to the light-emitting means when an integrated value obtained by integrating the digital data reaches a predetermined threshold value.
That is, the light-emission control apparatus controls the light-emission preformed by the light-emitting means, in accordance with the output value of the light-receiving means.
To achieve the object, a camera apparatus according to the present invention comprises: an image sensing section for capturing an object image; light-emitting means designed to stop emitting light in response to a light-emission stop request; light-receiving means for outputting a light-reception signal corresponding to an amount of light received; analog-to-digital converting means for converting the light-reception signal to digital data; and control means for outputting a light-emission stop request to light-emitting means, thereby causing the light-emitting means to stop emitting light, when an integrated value obtained by integrating the digital data reaches a predetermined threshold value.
In the camera apparatus, the light-emission stop request is output to the light-emitting means when an integrated value obtained by integrating the digital data reaches a predetermined threshold value.
That is, in this camera apparatus, the light-emitting means stops emitting light in accordance with the digital output value of the light-receiving means.
The light-emission control apparatus according to the invention comprises: light-receiving means for outputting a light-reception signal corresponding to an amount of light received; analog-to-digital converting means for converting the light-reception signal to digital data; and control means for outputting a light-emission stop request to light-emitting means, thereby causing the light-emitting means to stop emitting light, when an integrated value obtained by integrating the digital data reaches a predetermined threshold value. The apparatus can therefore make the light-emitting means stop emitting light when the integrated value reaches the predetermined threshold value.
That is, the light-emission control apparatus can control the termination of the light emission effected by the light-emitting means, in accordance with the digital data, i.e., the output value of the light-receiving means.
The output value of the light-receiving means is converted to digital data. The digital data, not analog data, is processed to control the termination of the light emission. The apparatus can therefore control the emission of light with high precision.
The camera apparatus of the present invention comprises: an image sensing section for capturing an object image; light-emitting means designed to stop emitting light in response to a light-emission stop request; light-receiving means for outputting a light-reception signal corresponding to an amount of light received; analog-to-digital converting means for converting the light-reception signal to digital data; and control means for outputting a light-emission stop request to light-emitting means, thereby causing the light-emitting means to stop emitting light, when an integrated value obtained by integrating the digital data reaches a predetermined threshold value.
In other words, with the camera apparatus the termination of the light emission effected by the light-emitting means can be controlled in accordance with the digital data, i.e., the output value of the light-receiving means.
The output value of the light-receiving means is converted to digital data, The digital data, not analog data, is processed to control the termination of the light emission. Therefore, the emission of light can be controlled with high precision in the camera apparatus.